Most of the conventional magnetic recording media are of the coated type. These media are produced by dispersing particles of magnetic oxides such as .gamma.-Fe.sub.2 O.sub.3, Co-doped .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, Co-doped Fe.sub.3 O.sub.4, a Berthollide compound of .gamma.-Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, CrO.sub.2, etc., or ferromagnetic alloy particles in an organic binder such as a vinyl chloride/vinyl acetate copolymer, a styrene/butadiene copolymer, an epoxy resin or polyurethane resin, applying the resulting coating solution to a non-magnetic base, and drying the coating. However, due to a recently increasing demand for higher density recording, researchers' attention has been drawn to magnetic recording media of thin metal film type that uses, as a magnetic recording layer, a thin ferromagnetic metal film. The film is formed by the vapor deposition such as vacuum deposition, sputtering or ion plating, or the plating such as electroplating or electrolessplating. Various efforts have been made to use such recording media on a commercial basis.
Most of the magnetic recording media of coated type use a metal oxide having a small saturation magnetization as a magnetic material. Therefore, an attempt to achieve high density recording by using a thinner magnetic recording medium results in a decreased signal output. However, with a magnetic recording medium of thin metal film type, a very thin magnetic recording layer can be formed by using a ferromagnetic metal having a greater saturation magnetization than that of the magnetic oxide without using a non-magnetic material such as a binder. This thinness is very advantageous for providing good electro-to-magnetic conversion characteristics. However, the thin metal film type magnetic recording medium has its own problems: (1) it develops a large amount of friction against the magnetic head, guide poles or other transport means when it is run to record, reproduce or erase magnetic signals, and hence wears easily; (2) it is easily attacked by corrosive environments; and (3) the magnetic recording layer may be damaged on impact during handling.
Some attempts have been made to solve these problems by forming a protective layer on the magnetic recording medium of thin metal film type. One such proposal is described in Japanese Patent Application (OPI) No. 75001/75 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") wherein a thin lubricant layer is formed on the metal film. According to this proposal, the friction coefficient between the magnetic head or guide poles and the metal film is reduced, providing a tape that runs consistently and which is least likely to be abraded. However, these advantages are quickly lost if the tape is used repeatedly. Another method is described in Japanese Patent Application (OPI) Nos. 39708/78 and 40505/78 wherein a lubricant protective layer made of a metal or metal oxide is formed on the thin metal film. However, even when using this method, the effect of the protective layer does not last long. When the tape is used repeatedly, the friction coefficient is increased rapidly or the thin magnetic metal film breaks. Still another method is described in Japanese Patent Application (OPI) No. 155010/79 wherein an overcoat of a high molecular film is formed on the metal film. However, if the overcoat is made of vinylidene chloride/acrylic ester copolymer and other known high molecular substances, the resulting film thickness is at least about 0.2 .mu.m and this causes spacing loss which in turn leads to reduced output in high density recording.
Further, most thin magnetic metal films are supported on a very smooth base to achieve high density recording. However, even when the lubricating methods described above are applied to such a smooth base, running properties, especially in highly humid atmospheres, and wear resistance of the base cannot satisfactorily be improved.